ABUNDANCES IN CH SUBGIANTS - EVIDENCE OF MASS-TRANSFER ONTO MAIN-SEQUENCE COMPANIONS

Carbon, oxygen, and s-process abundances, as well as abundances of oth er metals, such as iron, calcium, or nickel, are presented for a sampl e of nine CH subgiants. The abundances are derived from high-resolutio n, high-S/N spectra. The CH subgiants in this sample are found to have mild metal-deficiencies ([Fe/H] almost-equal-to 0.0 to -0.4), a range of s-process overabundances ([s-process/Fe] almost-equal-to +0.2 to 1.0), and C/O ratios from 0.4 to 2.0. When compared to the barium gian t stars, the CH subgiants tend to have larger C/O ratios, however, the barium giants have deep convective envelopes that are presumably abse nt from the CH subgiants, which lie on, or near, the main sequence. As the CH subgiants evolve up the red giant branch and develop deep conv ective envelopes, their carbon-rich atmospheres will be mixed with mat erial less abundant in C and their C/O ratios will decrease. It is thu s quite probable that the majority of the barium giant stars have evol ved from CH subgiant progenitors. The heavy-element abundance distribu tions of the CH subgiants studied here, as well as published analyses of other barium and CH giant stars, indicate that the s-process abunda nce enhancements are created by neutrons from the C-13(alpha, n)O-16 n eutron source.